1. Field of the Invention
The present invention relates to conformance additives, to conformance treatment fluids made therefrom, to methods of improving conformance in a well. In another aspect, the present invention relates to conformance additives comprising polymer and fibers, to conformance treatment fluids made therefrom, to methods of improving conformance in a well using such fluids.
2. Description of the Related Art
In the production of hydrocarbons from subterranean hydrocarbon bearing formations, poor vertical conformance results from the vertical juxtaposition of relatively high permeability geologic zones to relatively low permeability zones within the subterranean formation. Poor areal conformance results from the presence of high permeability streaks and high permeability anomalies within the formation matrix, such as vertical fractures and networks of the same, which have very high permeability relative to the formation matrix. Fluids generally exhibit poor flow profiles and sweep efficiencies in subterranean formations having poor vertical or areal conformance. Poor conformance is particularly a problem where vertical heterogeneity and/or fracture networks or other structural anomalies are in fluid communication with a subterranean wellbore across which fluids are injected or produced.
The prior art is replete with a number of attempts to remedy conformance problems. For example, U.S. Pat. Nos. 3,762,476; 3,981,363; 4,018,286; and 4,039,029 to Gall or Gall et al describe various processes wherein gel compositions are formed in high permeability zones of subterranean formations to reduce the permeability therein. According to U.S. Pat. No. 3,762,476, a polymer such as polyacrylamide is injected into a formation followed sequentially by a crosslinking agent. The sequentially injected slugs are believed to permeate the treatment zone of the formation and gel in situ.
U.S. Pat. Nos. 4,683,949 and 4,744,419 both to Sydansk et al., both note that it is generally held that effective polymer/crosslinking agent systems necessitate sequential injection of the gel components because gel systems mixed on the surface often set up before they can effectively penetrate the treatment region. Both Sydansk et al. patents further note that in practice, treatments such as that disclosed in U.S. Pat. No. 3,762,476 using sequentially injected gel systems have proven unsatisfactory because of the inability to achieve complete mixing and gelation in the formation. As a result, gels only form at the interface of the unmixed gel components and often in regions remote from the desired treatment region.
Both of the Sydansk et al. patents purport to overcome a then-existing need in the art for a gelation process capable of forming gels having a predetermined gelation rate, strength, and stability to satisfy the particular demands of a desired treatment region in a subterranean hydrocarbon-bearing formation, through the use of a high molecular weight water-soluble acrylamide polymer, a chromium III/carboxylate complex cross-linking agent.
U.S. Pat. No. 5,377,760 to Merrill notes that while the polymer system of Sydansk et al. '949 was an improvement over prior art systems which required sequential injection of the polymer components, difficulty was still encountered in employing the '949 polymer system to plug large fissures because the larger masses of polymer required often lack the necessary strength to resist the pressures to which they are exposed. Merrill proposes the incorporation of fibers in the polymer by mixing the fibers with the polymer solution at the surface.
U.S. Pat. No. 3,701,384 discloses a method of sealing thief zones in a subterranean formation by plugging pores with a solid material. A slurry of finely divided inorganic solids is injected into the formation together with an aqueous colloidal dispersion of a water-insoluble metal hydroxide in a dilute aqueous solution of a high-molecular-weight organic polymeric polyelectrolyte. The preferred polymer solution contains between about 0.01 and about 0.2 percent by weight of high molecular weight polyacrylamide or hydrolyzed polyacrylamide. At these concentrations, the dissolved polymer causes the suspended solids to flocculate, thereby blocking pores in the formation. The tested inorganic solids which interacted with the polymer solution to form strong solids included finely ground asbestos fibers and magnesium oxide. However, asbestos is undesirable for use today, due to its carcinogenicity.
Another approach taken by the prior art is to pump a slurry containing a mixture of flexible fibers and a bonding agent into highly permeable portions of a formation interval. An agent which precipitates or gels the bonding agent is then injected into the interval. The goal of the method is to build up a filter cake of fibers on the permeable formation as a result of the fibers being deposited out of the slurry as the slurry flows through, the permeable formation, and then bond the fibers of the filter cake in place. Examples of such a method are disclosed in U.S. Pat. Nos. 3,593,798, 3,949,811 and 3,462,958.
Larger fissures are bridged according to the disclosure of U.S. Pat. No. 2,708,973 by setting fibrous plants in place in the fissure, after which cement is added, thereby building on the framework of the plants.
While such a method can bridge larger gaps, the process is impractical for use in deep formations that extend over a large area.
U.S. Pat. No. 3,374,834 discloses a method of stabilizing earth formations by injecting an aqueous solution of gelling material which contains finely divided inert solids and needle-like crystals of silicate materials which act as a suspending agent to prevent premature settling out of the solids. The resulting gel does not, however, provide the desired combination of strength, economy, ease of mixing and ability to be readily introduced into a formation.
However, in spite of the advancements in the prior art, there still need for further innovation in the conformance improvement arts.
Specifically, Merrill's teaching of mixing the fibers with the polymer solution requires a multiplicity of storage and mixing tanks, and a metering system which must be operated during the operation of the well. Specifically, a first tank will store a water and polymer solution, a second tank will store a water and crosslinking solution, and a third tank will be used to mix fibers with polymer solution from the first tank to create a polymer/fiber slurry. This polymer/fiber slurry is then metered from the third tank and combined with cross-linking solution metered from the second tank to the well bore.
Thus, there is a need for a conformance additive which would allow for simplification of the mixing equipment.
There is another need a conformation method allowing for a simplification of the mixing equipment.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.